3d intraoral measurements using optical multiline method

ABSTRACT

A method for mapping a sensor pixel array to an illumination pixel array according to a surface forms a group map by assigning each pixel on the sensor array to a corresponding group of an ordered set of groups, each group defined by a set of p adjacent pixels on the illumination pixel array by projecting and recording at least n projected images from a first set of n binary patterns, with transitions between pixels in each of the n binary patterns only at group boundaries. At least m images from a second set of m binary patterns are projected and recorded, with one or more transitions between pixels in each of the m binary pattern offset from group boundaries. At least p multiline images are projected and recorded. Lines in the recorded multiline images are correlated with lines in the multiline images according to the group map.

FIELD OF THE INVENTION

The disclosure relates generally to the field of surface shape imagingand more particularly relates to intraoral surface imaging andmeasurement.

BACKGROUND OF THE INVENTION

Techniques have been developed for obtaining surface contour informationfrom various types of objects in medical, industrial, and otherapplications. Optical 3-dimensional (3-D) measurement methods provideshape and depth information using images obtained from patterns of lightdirected onto a surface. Various types of imaging methods generate aseries of light patterns and use focus or triangulation to detectchanges in surface shape over the illuminated area.

Fringe projection imaging uses patterned or structured light andtriangulation to obtain surface contour information for structures ofvarious types. In fringe projection imaging, a pattern of lines of aninterference fringe or grating is projected toward the surface of anobject from a given angle. The projected pattern from the surface isthen viewed from another angle as a contour image, taking advantage oftriangulation in order to analyze surface information based on theappearance of contour lines. Phase shifting, in which the projectedpattern is incrementally spatially shifted for obtaining additionalmeasurements at the new locations, is typically applied as part offringe projection imaging, used in order to complete the contour mappingof the surface and to increase overall resolution in the contour image.

Fringe projection imaging has been used effectively for surface contourimaging of solid, highly opaque objects and has been used for imagingthe surface contours for some portions of the human body and forobtaining detailed data about skin structure. However, a number oftechnical obstacles have prevented effective use of fringe projectionimaging of the tooth. One particular challenge with dental surfaceimaging relates to tooth translucency. Translucent or semi-translucentmaterials in general are known to be particularly troublesome for fringeprojection imaging. Subsurface scattering in translucent structures canreduce the overall signal-to-noise (S/N) ratio and shift the lightintensity, causing inaccurate height data. Another problem relates tohigh levels of reflection for various tooth surfaces. Highly reflectivematerials, particularly hollowed reflective structures, can effectivelyreduce the dynamic range of this type of imaging.

From an optical perspective, the structure of the tooth itself presentsa number of additional challenges for fringe projection imaging. Teethcan be wet or dry at different times and along different surfaces andportions of surfaces. Tooth shape is often irregular, with sharp edges.As noted earlier, teeth interact with light in a complex manner. Lightpenetrating beneath the surface of the tooth tends to undergosignificant scattering within the translucent tooth material. Moreover,reflection from opaque features beneath the tooth surface can alsooccur, adding noise that degrades the sensed signal and thus furthercomplicates the task of tooth surface analysis.

One corrective measure that has been attempted to make fringe projectionworkable for contour imaging of the tooth is application of a coatingthat changes the reflective characteristics of the tooth surface itself.To compensate for problems caused by the relative translucence of thetooth, conventional tooth contour imaging systems apply a paint orreflective powder to the tooth surface prior to surface contour imaging.For the purposes of fringe projection imaging, this added step enhancesthe opacity of the tooth and eliminates or reduces the scattered lighteffects noted earlier. However, there are drawbacks to this type ofapproach. The step of applying a coating powder or liquid adds cost andtime to the tooth contour imaging process. Because the thickness of thecoating layer is often non-uniform over the entire tooth surface,measurement errors readily result. More importantly, the appliedcoating, while it facilitates contour imaging, can tend to mask otherproblems with the tooth and can thus reduce the overall amount of usefulinformation that can be obtained.

Even where a coating or other type of surface conditioning of the toothis used, however, results can be disappointing due to the pronouncedcontours of the tooth surface. It can be difficult to provide sufficientamounts of light onto, and sense light reflected back from, all of thetooth surfaces. The different surfaces of the tooth can be oriented at90 degrees relative to each other, making it difficult to direct enoughlight for accurately imaging all parts of the tooth.

It can be appreciated that an apparatus and method that providesaccurate surface contour imaging of the tooth, without the need forapplying an added coating or other conditioning of the tooth surface forthis purpose, would help to speed reconstructive dentistry and couldhelp to lower the inherent costs and inconvenience of conventionalmethods, such as those for obtaining a cast or other surface profile fora crown, implant, or other restorative structure.

SUMMARY OF THE INVENTION

An object of the present invention is to advance the art of surfacecontour detection of teeth and related intraoral structures. Embodimentsof the present invention provide 3-D surface information about a toothby illuminating the tooth surface with an arrangement of light patternsthat help to more closely map pixel locations on a digital imaging arraywith pixel locations from an illumination device. Advantageously, thepresent invention can be used with known illumination and imagingcomponent arrangements and is adapted to help reduce ambiguity of sensedpatterns when compared against conventional contour detection methods.

These objects are given only by way of illustrative example, and suchobjects may be exemplary of one or more embodiments of the invention.Other desirable objectives and advantages inherently achieved by thedisclosed invention may occur or become apparent to those skilled in theart. The invention is defined by the appended claims.

According to one aspect of the invention, there is provided a method formapping a sensor pixel array to an illumination pixel array according toa surface, the method executed at least in part on a computer andcomprising: forming a group map by assigning each pixel in a pluralityof pixels on the sensor array to a corresponding group of an ordered setof groups, wherein each group is defined by a set of p adjacent pixelson the illumination pixel array and wherein each group is defined by agroup boundary by: projecting and recording at least n images from afirst set of n binary patterns onto the surface, wherein a bright todark or dark to bright transition between pixels in each of the n binarypatterns occurs only at one or more of the group boundaries; projectingand recording at least m images from a second set of m binary patternsonto the surface, wherein one or more bright to dark or dark to brighttransitions between pixels in each of the m binary patterns are offsetfrom one or more of the group boundaries; projecting and recording atleast p multiline images onto the surface, wherein each multiline imageprojects a line within each group; correlating lines in the recordedmultiline images with lines in the projected multiline images accordingto the group map; and storing the correlation in a computer-accessiblememory, wherein n and m are integers greater than or equal to 1 and p isan integer greater than or equal to 2.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings. The elements of the drawings are not necessarilyto scale relative to each other.

FIG. 1 is a schematic diagram that shows mapping a sensor pixel array toan illumination array according to a surface.

FIG. 2A shows illumination of a tooth surface with a single line oflight.

FIG. 2B shows illumination of a tooth surface with multiple lines oflight.

FIG. 3 is a logic flow diagram that shows a sequence for obtainingsurface contour image data according to an embodiment of the presentinvention.

FIG. 4 is a schematic diagram showing an imaging apparatus.

FIG. 5 is a logic flow diagram that shows an image projection andrecording sequence.

FIG. 6 is a schematic diagram that shows part of a row of pixels on theimaging sensor array.

FIG. 7 is a schematic diagram that shows in-phase binary projectedpatterns for group mapping.

FIG. 8 is a schematic diagram that shows a binary projected pattern of asecond out-of-phase set.

FIG. 9 shows a single projected binary pattern.

FIG. 10A shows a portion of the illumination array for forming amultiline image.

FIG. 10B shows another portion of the illumination array for forming amultiline image.

FIG. 11 is a plan view of an exemplary multiline image.

FIG. 12 is a plan view of a projected multiline image on a tooth.

FIG. 13 is another plan view of a projected multiline image on a tooth.

FIG. 14 is a schematic diagram showing how data from binary patternimages and multiline images are combined.

FIGS. 15A and 15B compare results for uncoated and coated teeth.

FIG. 16 is a difference map combining the results of FIGS. 15A and 15B.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the preferred embodiments ofthe invention, reference being made to the drawings in which the samereference numerals identify the same elements of structure in each ofthe several figures. Where they are used, the terms “first”, “second”,and so on, do not necessarily denote any ordinal, sequential, orpriority relation, but are simply used to more clearly distinguish oneelement or set of elements from another.

The schematic diagram of FIG. 1 shows, with the example of a single lineof light L, how patterned light is used for obtaining surface contourinformation. A mapping is obtained as an illumination array 10 directs apattern of light onto a surface 20 and a corresponding image of a lineL′ is formed on an imaging sensor array 30. Each pixel 32 on imagingsensor array 32 maps to a corresponding pixel 12 on illumination array10 according to modulation by surface 20. Shifts in pixel position, asrepresented in FIG. 1, yield useful information about the contour ofsurface 20. It can be appreciated that the basic pattern shown in FIG. 1can be implemented in a number of ways, using a variety of illuminationsources and sequences and using one or more different types of sensorarrays 30. Illumination array 10 can utilize any of a number of types ofarrays used for light modulation, such as a liquid crystal array ordigital micromirror array, such as that provided using the Digital LightProcessor or DLP device from Texas Instruments, Dallas, Tex. This typeof spatial light modulator is used in the illumination path to changethe light pattern as needed for the mapping sequence.

FIGS. 2A and 2B show aspects of one problem with conventional approachesfor using patterned light to obtain surface structure information fromthe human tooth. FIG. 2A shows illumination with a single line of light14 onto the tooth, with pronounced shifting of the illumination at thetooth edges. Projection of a single line in this manner, scanned acrossthe tooth and imaged at numerous points during the scan, can provideaccurate information about portions of the surface area; however, someinformation is lost even with this method, such as where line segmentsare separated from each other. FIG. 2B shows surface imaging using apattern with multiple lines of light. Where there are abrupt transitionsalong the surface, it can be difficult to positively identify thesegments that correspond to each projected line and mismatches caneasily occur, leading to inaccurate conclusions about surfacecharacteristics. For example, it can be difficult to determine whetherline segment 16 is from the same line of illumination as line segment 18or adjacent line segment 24.

Embodiments of the present invention address the problem of surfacecontour mapping using a sequence of projected images that help to bettercorrelate pixels on the imaging sensor array with projected lines fromthe illumination array. To do this, embodiments of the present inventionuse an arrangement of binary images to group pixels on the imagingsensor array with corresponding pixels on the illumination pixel array.A group map is formed by assigning pixels on the sensor array to anordered set of groups, each group having a fixed number of pixels.

Referring to the flow diagram of FIG. 3, there is shown a sequence ofimage projection, detection, and processing steps used for surfacecontour detection and executed at least in part on a computer accordingto an embodiment of the present invention. In an image capture step 40,the operator positions the imaging apparatus and captures a series ofimages, as described subsequently. The images consist of a number n ofbinary patterns 46 and m binary patterns 48 and p multiline images 54and can be captured in any order. Once the images are captured, a pixelassignment step 44 executes, in which pixels on the image sensor arrayare assigned to a group map that corresponds to pixels on theillumination array. Images for the group mapping are from binarypatterns 46 and 48, described in more detail subsequently. An additionaldark image 36, with no illumination, and flat image 38 with full frameillumination are also obtained to help in signal processing, asdescribed subsequently.

Continuing with the sequence of FIG. 3, a set of p multiline images 54is also obtained, from which peak locations, that is, locations ofhighest intensity, can be detected in a location detection step 50. Amapping step 60 then forms and stores the contour image in a memory,such as in a temporary display memory that is associated with a displaymonitor, for example.

Relative to FIG. 1, a binary pattern has one or more bright bands thatare two or more pixels wide on illumination array 10. A multiline imagehas one or more bright bands that are one pixel wide on illuminationarray 10. The multiline image has at least one bright-to-dark ordark-to-bright transition within each group of pixels.

The schematic diagram of FIG. 4 shows an imaging apparatus 70 forprojecting and imaging the binary patterns 46 and 48 and multilineimages 54. A control logic processor 80, or other type of computercontrols the operation of illumination array 10 and imaging sensor array30. Image data from surface 20, such as from a tooth 22, is obtainedfrom imaging sensor array 30 and stored in a memory 72. Control logicprocessor 80 processes the received image data and stores the mapping inmemory 72. The resulting image from memory 72 is then optionallydisplayed on a display 74. Memory 72 may also include a display buffer.

The logic flow diagram of FIG. 5 shows the image projection and capturesequence described as image capture step 40 in FIG. 3 and using theimaging apparatus 70 of FIG. 4 in more detail. A first binary patternrecording step 62 records at least n images from a first set of n binarypatterns projected onto the surface, in which transitions between pixelsoccur only at group boundaries, as described subsequently. This set of nimages is described as being “in-phase” with the group arrangement. Asecond binary pattern recording step 64 then records m binary patternsprojected onto the surface, in which one or more transitions betweenpixels in each of the m patterns are offset from group boundaries, againdescribed in more detail subsequently. This set of m images is describedas being “out-of-phase” with the group arrangement, with at least onetransition within a group. A dark and flat image recording step 65 thenrecords dark field and flat field images. The combination of imagesrecorded from recording steps 62, 64, and 65 are then used for formingthe group map in pixel assignment step 44 of FIG. 3. A multiline imagerecording step 66 projects onto the surface and records at least pmultiline images, as described in more detail subsequently. Followingimage capture, a correlation step 68 then correlates surface positionswith pixel positions on image sensor array 30 as part of mapping step 60in FIG. 3. An optional display step 82 then displays the surface contourobtained from the mapping.

Forming the Group Map

Schematic diagrams of FIGS. 6, 7, and 8 show various aspects of theprocess for forming the group map according to an embodiment of thepresent invention. FIG. 6 shows part of a row of pixels 32 on imagingsensor array 30 corresponding to positions on surface 20. Each group hasa predetermined number p of adjacent pixels 32, with eight pixels 32 pergroup in the example mapping that is shown. Vertical dashed lines inFIGS. 6-8 indicate group boundaries. At a group boundary, wherein eachgroup has p pixels numbered from 0, 1, 2, . . . (p−1), the (p−1)th pixelof one group is adjacent to the 0th pixel of the next, or adjacent,group in the row; the space between these two adjacent pixels, with onepixel in each of two adjacent groups, defines a group boundary. Thegroup boundary is considered to be “shared” by two adjacent groups. Twosequences of projected binary patterns are used to establish the groupmap. The schematic diagram of FIG. 7 shows the first pattern. Here, nimages from a set of n binary patterns are projected from illuminationarray 10 in which each row is arranged according to groups.Representative eight-pixel groups G8, G7, G6, and G5 are shown, numberedin descending order from right to left in this example. Two of the nbinary patterns 46 a and 46 b are shown, with binary 1, 0 representationshown for respective dark (off or 0)/bright (on or 1) bands that havetransitions from bright to dark or, alternately, from dark to bright, atgroup boundaries. In the example shown at enlarged portion E, a 0110portion of the binary pattern 46 a is represented, with transitionsbetween 0 and 1 occurring only at group boundaries. Binary pattern 46 bis the next binary pattern in sequence, changing only one bit from thebinary pattern at 46 a. Consistent with an embodiment of the presentinvention, the successive binary patterns are arranged in a sequencethat emulates a Gray code, in which each successive pattern (x) changesby only one bit from the previous pattern (x−1). This use of a Gray codeemulation is advantaged for helping to reduce ambiguity in determiningwhich corresponding pixel on imaging sensor array 30 maps to a groupdefined on illumination array 10 (FIG. 1). Bright bands in the binarypatterns 46 a and 46 b, corresponding with binary number 1 in FIGS. 7and 8, have a width that is in integer increments of a group of pixels,so that a bright band will be as wide as one, two, or more than twogroups of pixels from the illuminator array. In the example of FIG. 7,in which a group has 8 pixels, a bright band in the binary pattern 46 aor 46 b is 8, 16, 24, 32, or some other integer multiple of 8 pixelswide.

The schematic diagram of FIG. 8 shows projection of one of the secondset of m binary patterns 48. Here, one or more of the binary 0/1 or 1/0transitions between pixels are offset from group boundaries. In theexample shown, group G7 spans across the corresponding transition thatis offset from its boundary with group G6. Similarly, a transition isoffset from the border of group G5, splitting pixels in this group intothose on one side of the transition and those on the other. This use ofan offset or out-of-phase pattern is a feature of embodiments of thepresent invention and acts as a further check on group boundaries, tohelp resolve possible ambiguity between group assignments. FIG. 9 showsa single projected binary pattern 46 relative to a typical tooth.

Consistent with an embodiment of the present invention, an analog filteris applied to each of the binary pattern images. This has been found tobe of value in areas of low signal content. Alternately, thresholdingusing a digital filter can be employed for this purpose.

There is some level of signal (a “cut-off point”) in the flat image 38(FIG. 3) that can be too low for accurate comparisons. This level cansimply be set as a parameter for the processing software. It can also becalculated adaptively by finding all the peaks in the multiline image,as described subsequently, and noting the “flat” values at those peakpositions. Pixels with levels below this cutoff point are simplydeclared to be indeterminate, having unknown states, and are notprocessed further.

After thresholding, the n block images are combined at each pixel toform an n-bit number. This number is then translated through the inverseof an encoding table to identify the corresponding group number. In theabsence of errors, this completes the block image processing.

Geometrically, when moving from one side of the image to the other alonga row, the group number must change monotonically. (The numbers ondifferent rows may not align, but within each row, they are monotonic.)This makes it possible to ‘proofread’ the group numbers on each row,discarding places where noise has disturbed the expected monotonicincrease of group number.

Multiline Images

As was noted with respect to the sequences shown in FIGS. 3 and 5, a setof at least p multiline images is projected onto the surface, inaddition to the n in-phase and m out-of-phase images. The schematicdiagram of FIG. 10A shows, for a single row of illumination array 10, aportion of a first multiline image 54 a in which the left-most pixel ineach group is illuminated to form a line. FIG. 10B shows anothermultiline image 54 b in which the next pixel in each group isilluminated. Where each group has 8 pixels, as in the examples shownherein, this sequence repeats so that there are at least 8 multilineimages, one for each pixel in each group. Transitions from dark to lightor from light to dark are only with respect to a single pixel width in amultiline image; each bright band of light that forms a line is a singlepixel wide. Each multiline image projects a single line within eachgroup, so that there is at least one bright-to-dark or dark-to-brighttransition between adjacent group boundaries in a multiline image. Ingeneral, where each group has a number p adjacent pixels, at least pmultiline images are projected onto the surface and recorded. Inaddition, more than 8 multiline images can be projected and recorded, incyclical or other sequencing arrangement. FIG. 11 shows a multilineimage 54 with a line 84 within each group as projected from illuminationarray 10. FIGS. 12 and 13 show exemplary multiline images 54 asprojected onto the surface 20 and recorded by imaging sensor array 30.The dashed line Q in FIG. 12 indicates one row of pixels on imagingsensor array 30.

Consistent with an embodiment of the present invention, each of themultiline images is analyzed as a set of independent rows, to locateeach intensity peak in the row. This is done in two steps. Initially, acombination of smoothing filter and differentiating filter locatespixels where there is a peak signal. Then, a parabola is fit to theobserved points around the identified pixel in order to locate the peakwith sub-pixel accuracy. The background around the peak is alsoestimated to provide additional information on relative peak height. Acandidate peak can be dropped from the list of peaks if it is too weakor too close to another peak. The result of the analysis is a long peaklist (30,000 to 100,000 for a typical imaging sensor array) of preciselocations where intensity peaks were observed.

Combining the Group Map and Peak List

In the absence of noise or errors, combination of group and peak data isdriven by the list of peaks, which contains the peak location in x and y(i.e. pixel location along the row and the row number), the peak height,the peak width, and the image from which it came (multiline images 1 top). For each peak, the group number from the nearest pixel in the GroupMap is retrieved. The group number and image number are combined tocalculate the line on the illuminator, 1 to 480 in a 480 line image.This gives three essential “pixel positions” for the peak: the x and ylocation on the imager and the x location on the illuminator, just aswould be obtained from a single projected point.

Next, an approximate position of the point on the tooth or other surfaceis calculated, using the three pixel positions and calibrationparameters. These approximate positions are processed, using informationknown from calibration, to determine an accurate location (x, y, z) onthe surface. All of these locations form the point cloud, which is thefinal output of the combination algorithm.

The in-phase binary patterns 46 and out-of-phase binary patterns 48 arecombined to improve the accuracy of the mapping and to compensate andidentify various physical effects that might otherwise induce errors inthe Group Map. For the explanation that follows:

(1) the term “phase” relates to the image number (1−p) from which a peakcame;

(2) the numerical labeling of illuminator lines is assumed to increasefrom right to left on the imaging sensor array; a monotonic rule statesthat the group number must increase from right to left along a row; and

(3) there are assumed to be multiple (at least 2 or 3) imaging sensorarray pixels for every illuminator array pixel.

Referring to the schematic diagram of FIG. 14, a portion of anout-of-phase binary pattern 48 is shown, with corresponding lines from afirst captured image frame from the multiline images represented. Anumber of representative lines L185, L193, L200, and L201 are shown. Aportion of the group mapping is also shown for groups G24, G25, and G26.Corresponding illuminator array pixel center positions 94 are alsoshown.

Lines L193 to L200 are in group G25. The out-of-phase binary pattern 48changes between groups, as described previously. An arrow A marks a peakobserved in a phase 1 multiline image. (The phase numbers count fromright to left in this example arrangement.) Errant group codes can bedetected in a number of ways, including the following:

(i) The group code should change only near phases 1 and 8. For peaks inphases 2-7, all the pixels around a peak center should have the samegroup code.

(ii) Assume there is a peak in a phase 1 image and the group code isG25. That must be line L193 on the illuminator array, unless there is anerror and is actually group G24, misread. If this is the case, it isline L185. Alternately, it could be line L201 in group 26. However, theout-of-phase signal of binary pattern 48 is unambiguously high aroundline L193 and low around lines L185 and L201. Checking the out-of-phasesignal verifies the group code for phases 1 and 8, as well as phases 2and 7.

(iii) Keeping track of the group code associated with each peak on arow; from right to left, the group codes should increase monotonically.A code may be skipped, but the group number should not decrease. If adecrease is observed, a potential problem is indicated.

Dark and Flat Images

Dark and flat images 36 and 38 are obtained as described in the sequenceof FIG. 3. These images can be averaged to provide a measure ofintensity that is used as a threshold to differentiate bright from darkintensities to help improve the signal mapping in pixel assignment step44 (FIG. 3).

It is noted that the sequence of image projections and recording can befollowed in any suitable order for the methods of the present invention.Moreover, multiline images and binary patterns can be interspersed,rather than obtained in any fixed order.

FIGS. 15A and 15B compare results of processing using the method of thepresent invention for an uncoated tooth 90 and for a coated tooth 92,that is, a tooth coated with a powder or other material, as is employedwith tooth surface imaging systems that have been commerciallyavailable. As shown, results for uncoated tooth 90 compare favorably tothose for coated tooth 92, without the need to prepare the tooth.

FIG. 16 shows a difference map 98 from combining the images for uncoatedand coated teeth 90 and 92.

Consistent with at least one embodiment of the present invention, acomputer executes a program with stored instructions that perform onimage data accessed from an electronic memory. As can be appreciated bythose skilled in the image processing arts, a computer program of anembodiment of the present invention can be utilized by a suitable,general-purpose computer system, such as a personal computer orworkstation, as well as by a microprocessor or other dedicated processoror programmable logic device. However, many other types of computersystems can be used to execute the computer program of the presentinvention, including networked processors. The computer program forperforming the method of the present invention may be stored in acomputer readable storage medium. This medium may comprise, for example;magnetic storage media such as a magnetic disk (such as a hard drive) ormagnetic tape or other portable type of magnetic disk; optical storagemedia such as an optical disc, optical tape, or machine readable barcode; solid state electronic storage devices such as random accessmemory (RAM), or read only memory (ROM); or any other physical device ormedium employed to store a computer program. The computer program forperforming the method of the present invention may also be stored oncomputer readable storage medium that is connected to the imageprocessor by way of the internet or other communication medium. Thoseskilled in the art will readily recognize that the equivalent of such acomputer program product may also be constructed in hardware.

It is understood that the computer program product of the presentinvention may make use of various image manipulation algorithms andprocesses that are well known. It will be further understood that thecomputer program product embodiment of the present invention may embodyalgorithms and processes not specifically shown or described herein thatare useful for implementation. Such algorithms and processes may includeconventional utilities that are within the ordinary skill of the imageprocessing arts. Additional aspects of such algorithms and systems, andhardware and/or software for producing and otherwise processing theimages or co-operating with the computer program product of the presentinvention, are not specifically shown or described herein and may beselected from such algorithms, systems, hardware, components andelements known in the art.

In the context of the present disclosure, the act of “recording” imagesmeans storing image data in some type of memory circuit in order to usethis image data for subsequent processing. The recorded image dataitself may be stored more permanently or discarded once it is no longerneeded for further processing. An “ordered set” has its conventionalmeaning as used in set theory, relating to a set whose elements have anon-ambiguous ordering, such as the set of natural numbers that areordered in an ascending sequence, for example.

It is noted that the term “memory”, equivalent to “computer-accessiblememory” in the context of the present disclosure, can refer to any typeof temporary or more enduring data storage workspace used for storingand operating upon image data and accessible to a computer system. Thememory could be non-volatile, using, for example, a long-term storagemedium such as magnetic or optical storage. Alternately, the memorycould be of a more volatile nature, using an electronic circuit, such asrandom-access memory (RAM) that is used as a temporary buffer orworkspace by a microprocessor or other control logic processor device.Display data, for example, is typically stored in a temporary storagebuffer that is directly associated with a display device and isperiodically refreshed as needed in order to provide displayed data.This temporary storage buffer can also be considered to be a memory, asthe term is used in the present disclosure. Memory is also used as thedata workspace for executing and storing intermediate and final resultsof calculations and other processing. Computer-accessible memory can bevolatile, non-volatile, or a hybrid combination of volatile andnon-volatile types. Computer-accessible memory of various types isprovided on different components throughout the system for storing,processing, transferring, and displaying data, and for other functions.

The invention has been described in detail with particular reference toa presently preferred embodiment, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. The presently disclosed embodiments are thereforeconsidered in all respects to be illustrative and not restrictive. Thescope of the invention is indicated by the appended claims, and allchanges that come within the meaning and range of equivalents thereofare intended to be embraced therein.

What is claimed is:
 1. A method for mapping a sensor pixel array to anillumination pixel array according to a surface, comprising: forming agroup map by assigning each pixel in a plurality of pixels on the sensorarray to a corresponding group of an ordered set of groups, wherein eachgroup is defined by a set of p adjacent pixels on the illumination pixelarray and wherein each group is defined by a group boundary by: (a)projecting and recording at least n images from a first set of n binarypatterns onto the surface, wherein a bright-to-dark or dark-to-brighttransition between pixels in each of the n binary patterns occurs onlyat one or more of the group boundaries; and (b) projecting and recordingat least m images from a second set of m binary patterns onto thesurface, wherein one or more bright-to-dark or dark-to-brighttransitions between pixels in each of the m binary patterns are offsetfrom one or more of the group boundaries; projecting and recording atleast p multiline images onto the surface, wherein each multiline imageprojects a line within each group; correlating lines in the recordedmultiline images with lines in the projected multiline images accordingto the group map; and storing the correlation in a computer-accessiblememory, wherein n and m are integers greater than or equal to 1 and p isan integer greater than or equal to
 2. 2. The method of claim 1 furthercomprising generating surface contour data according to the storedcorrelation.
 3. The method of claim 1 wherein the ratio of longest toshortest run lengths for the first set of n binary patterns is less than2^(n-4).
 4. The method of claim 1 wherein the first set of n binarypatterns is projected so that each successive pattern changes by onlyone bit from the previous pattern.
 5. The method of claim 1 wherein theratio of longest to shortest run lengths for the first set of n binarypatterns is less than 2^(n-4) and wherein the first set of n binarypatterns is projected so that each successive pattern changes by onlyone bit from the previous pattern.
 6. The method of claim 1 wherein theillumination pixel array is a liquid crystal device.
 7. The method ofclaim 1 wherein the illumination pixel array is a digital micromirrorarray device.
 8. The method of claim 1 wherein forming the group mapfurther comprises obtaining and recording at least one dark field imageand at least one flat field image.
 9. The method of claim 2 furthercomprising displaying the surface according to the surface contour data.10. A method for mapping a line of pixels in a sensor pixel array to aline of pixels in an illumination pixel array according to a surface,comprising: defining an ordered sequence of groups, wherein each groupis defined by a set of p pixels that are adjacent along the line on theillumination pixel array, wherein p is an integer greater than or equalto 2; assigning pixels along the line of pixels in the sensor pixelarray to the defined groups by projecting and recording a first set of aplurality of binary patterns wherein transitions are indicative of groupboundaries, projecting and recording a second set of one or more binarypatterns wherein one or more transitions in the second set are offsetfrom group boundaries, and projecting and recording at least one darkfield image and at least one flat field image; recording at least pmultiline images projected onto the surface, wherein each of themultiline images projects a single line of light at a time to eachdefined group of pixels; correlating lines in the recorded multilineimages with lines in the projected multiline images according to thegroup assignment and the at least one dark and flat field images; andstoring the correlation as a mapping in a computer-accessible memory.11. The method of claim 10 wherein the surface is a tooth.
 12. Themethod of claim 10 wherein the first set of n binary patterns isprojected so that each successive pattern changes by only one bit fromthe previous pattern.
 13. The method of claim 10 wherein the ratio oflongest to shortest run lengths for the first set of n binary patternsis less than 2^(n-4). and wherein the first set of n binary patterns isprojected so that each successive pattern changes by only one bit fromthe previous pattern.
 14. The method of claim 10 wherein theillumination pixel array is a liquid crystal device.
 15. The method ofclaim 10 wherein the illumination pixel array is a digital micromirrorarray device.
 16. The method of claim 10 further comprising displayingthe surface according to the stored mapping.
 17. A method for forming asurface contour image, comprising: forming a group map by assigning eachpixel in a plurality of pixels on the sensor array to a correspondinggroup of an ordered set of groups, wherein each group is defined by aset of p adjacent pixels in a row on the illumination pixel array andwherein two adjacent groups share a group boundary by: (a) projectingand recording at least n images from a first set of n binary patternsonto the surface, wherein a bright-to-dark or dark-to-bright transitionbetween pixels in each of the n binary patterns occurs only at the groupboundary; and (b) projecting and recording at least m images from asecond set of m binary patterns onto the surface, wherein one or morebright-to-dark or dark-to-bright transitions between pixels in each ofthe m binary patterns are offset from the group boundary; projecting andrecording at least p multiline images onto the surface, wherein eachmultiline image has, within each group of pixels in the ordered set ofgroups within the row, a single bright pixel; correlating lines in therecorded multiline images with lines in the projected multiline imagesaccording to the group map, wherein n and m are integers greater than orequal to 1 and p is an integer greater than or equal to 2; storing thecorrelation in a computer-accessible memory; and displaying the surfacecontour image formed according to the stored correlation.
 18. The methodof claim 17 wherein the first set of n binary patterns is projected sothat each successive pattern changes by only one bit from the previouspattern.
 19. The method of claim 17 wherein forming the group mapfurther comprises obtaining and recording at least one dark field imageand at least one flat field image.